[wasm-gc] Introduce extern null type noextern

noextern is the abstract null type for the extern type.

Bug: v8:7748
Change-Id: I03ac0daf3051f479e096f3d05f4fa7cbf03968f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3810191Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82276}

src/wasm/function-body-decoder-impl.h

@@ -239,6 +239,7 @@ HeapType read_heap_type(Decoder* decoder, const byte* pc,
       case kArrayRefCode:
       case kAnyRefCode:
       case kNoneCode:
+      case kNoExternCode:
       case kNoFuncCode:
         if (!VALIDATE(enabled.has_gc())) {
           DecodeError<validate>(
@@ -317,6 +318,7 @@ ValueType read_value_type(Decoder* decoder, const byte* pc,
     case kArrayRefCode:
     case kAnyRefCode:
     case kNoneCode:
+    case kNoExternCode:
     case kNoFuncCode:
       if (!VALIDATE(enabled.has_gc())) {
         DecodeError<validate>(

src/wasm/value-type.h

@@ -72,6 +72,7 @@ class HeapType {
     kStringViewIter,          // shorthand: z.
     kNone,                    //
     kNoFunc,                  //
+    kNoExtern,                //
     // This value is used to represent failures in the parsing of heap types and
     // does not correspond to a wasm heap type. It has to be last in this list.
     kBottom
@@ -103,6 +104,8 @@ class HeapType {
         return HeapType(kStringViewIter);
       case ValueTypeCode::kNoneCode:
         return HeapType(kNone);
+      case ValueTypeCode::kNoExternCode:
+        return HeapType(kNoExtern);
       case ValueTypeCode::kNoFuncCode:
         return HeapType(kNoFunc);
       default:
@@ -171,6 +174,8 @@ class HeapType {
         return std::string("stringview_iter");
       case kNone:
         return std::string("none");
+      case kNoExtern:
+        return std::string("noextern");
       case kNoFunc:
         return std::string("nofunc");
       default:
@@ -208,6 +213,8 @@ class HeapType {
         return mask | kStringViewIterCode;
       case kNone:
         return mask | kNoneCode;
+      case kNoExtern:
+        return mask | kNoExternCode;
       case kNoFunc:
         return mask | kNoFuncCode;
       default:
@@ -430,6 +437,7 @@ class ValueType {
   // If {this} is (ref null $t), returns (ref $t). Otherwise, returns {this}.
   constexpr ValueType AsNonNull() const {
     if (is_reference_to(HeapType::kNone) ||
+        is_reference_to(HeapType::kNoExtern) ||
         is_reference_to(HeapType::kNoFunc)) {
       // Non-null none type is not a valid type.
       return ValueType::Primitive(kBottom);
@@ -556,6 +564,8 @@ class ValueType {
             return kStringViewIterCode;
           case HeapType::kNone:
             return kNoneCode;
+          case HeapType::kNoExtern:
+            return kNoExternCode;
           case HeapType::kNoFunc:
             return kNoFuncCode;
           default:
@@ -701,6 +711,8 @@ constexpr ValueType kWasmStringViewWtf16 =
 constexpr ValueType kWasmStringViewIter =
     ValueType::RefNull(HeapType::kStringViewIter);
 constexpr ValueType kWasmNullRef = ValueType::RefNull(HeapType::kNone);
+constexpr ValueType kWasmNullExternRef =
+    ValueType::RefNull(HeapType::kNoExtern);
 constexpr ValueType kWasmNullFuncRef = ValueType::RefNull(HeapType::kNoFunc);
 
 // Constants used by the generic js-to-wasm wrapper.

src/wasm/wasm-constants.h

@@ -39,6 +39,7 @@ enum ValueTypeCode : uint8_t {
   kFuncRefCode = 0x70,
   // TODO(7784): Switch to official opcodes once they are aligned with the
   // stringref proposal for nofunc and noextern.
+  kNoExternCode = 0x69,
   kNoFuncCode = 0x68,
   kExternRefCode = 0x6f,
   // typed-funcref and GC proposal types

src/wasm/wasm-subtyping.cc

@@ -107,17 +107,18 @@ HeapType::Representation NullSentinel(HeapType type, const WasmModule* module) {
     case HeapType::kData:
     case HeapType::kArray:
     case HeapType::kAny:
-    case HeapType::kExtern:  // TODO(mliedtke): Add noextern.
     case HeapType::kString:
     case HeapType::kStringViewWtf8:
     case HeapType::kStringViewWtf16:
     case HeapType::kStringViewIter:
       return HeapType::kNone;
+    case HeapType::kExtern:
+    case HeapType::kNoExtern:
+      return HeapType::kNoExtern;
     case HeapType::kFunc:
     case HeapType::kNoFunc:
       return HeapType::kNoFunc;
     default:
-      // TODO(mliedtke): Add noextern.
       return module->has_signature(type.ref_index()) ? HeapType::kNoFunc
                                                      : HeapType::kNone;
   }
@@ -126,8 +127,8 @@ HeapType::Representation NullSentinel(HeapType type, const WasmModule* module) {
 bool IsNullSentinel(HeapType type) {
   switch (type.representation()) {
     case HeapType::kNone:
+    case HeapType::kNoExtern:
     case HeapType::kNoFunc:
-      // TODO(mliedtke): Add noextern.
       return true;
     default:
       return false;
@@ -228,11 +229,15 @@ V8_NOINLINE V8_EXPORT_PRIVATE bool IsHeapSubtypeOfImpl(
     case HeapType::kNone:
       // none is a subtype of every non-func, non-extern reference type under
       // wasm-gc.
-      // TODO(mliedtke): Break-up extern and nullref subtyping.
       if (super_heap.is_index()) {
         return !super_module->has_signature(super_heap.ref_index());
       }
-      return super_heap != HeapType::kFunc && super_heap != HeapType::kNoFunc;
+      return super_heap != HeapType::kFunc && super_heap != HeapType::kNoFunc &&
+             super_heap != HeapType::kExtern &&
+             super_heap != HeapType::kNoExtern;
+    case HeapType::kNoExtern:
+      return super_heap == HeapType::kNoExtern ||
+             super_heap == HeapType::kExtern;
     case HeapType::kNoFunc:
       // nofunc is a subtype of every funcref type under wasm-gc.
       if (super_heap.is_index()) {
@@ -268,6 +273,7 @@ V8_NOINLINE V8_EXPORT_PRIVATE bool IsHeapSubtypeOfImpl(
     case HeapType::kBottom:
       UNREACHABLE();
     case HeapType::kNone:
+    case HeapType::kNoExtern:
     case HeapType::kNoFunc:
       // Abstract null types are not supertypes for any index type.
       return false;
@@ -391,6 +397,7 @@ HeapType::Representation CommonAncestorWithGeneric(HeapType heap1,
           return HeapType::kAny;
         case HeapType::kFunc:
         case HeapType::kExtern:
+        case HeapType::kNoExtern:
         case HeapType::kNoFunc:
           UNREACHABLE();
         default:
@@ -410,6 +417,7 @@ HeapType::Representation CommonAncestorWithGeneric(HeapType heap1,
           return HeapType::kAny;
         case HeapType::kFunc:
         case HeapType::kExtern:
+        case HeapType::kNoExtern:
         case HeapType::kNoFunc:
           UNREACHABLE();
         default:
@@ -430,6 +438,7 @@ HeapType::Representation CommonAncestorWithGeneric(HeapType heap1,
           return HeapType::kAny;
         case HeapType::kFunc:
         case HeapType::kExtern:
+        case HeapType::kNoExtern:
         case HeapType::kNoFunc:
           UNREACHABLE();
         default:
@@ -452,6 +461,7 @@ HeapType::Representation CommonAncestorWithGeneric(HeapType heap1,
         case HeapType::kEq:
         case HeapType::kAny:
         case HeapType::kExtern:
+        case HeapType::kNoExtern:
           UNREACHABLE();
         case HeapType::kNoFunc:
           return HeapType::kNoFunc;
@@ -462,6 +472,11 @@ HeapType::Representation CommonAncestorWithGeneric(HeapType heap1,
                      ? heap2.representation()
                      : HeapType::kBottom;
       }
+    case HeapType::kNoExtern:
+      return heap2.representation() == HeapType::kExtern ? HeapType::kExtern
+                                                         : HeapType::kNoExtern;
+    case HeapType::kExtern:
+      return HeapType::kExtern;
     default:
       UNREACHABLE();
   }

test/cctest/wasm/test-gc.cc

@@ -1546,7 +1546,7 @@ WASM_COMPILED_EXEC_TEST(CallAbstractNullTypeImplicitConversion) {
       {kWasmDataRef.AsNullable(), kNoneCode},
       {kWasmArrayRef.AsNullable(), kNoneCode},
       {kWasmAnyRef, kNoneCode},
-      {kWasmExternRef, kNoneCode},
+      {kWasmExternRef, kNoExternCode},
       {refNull(0), kNoneCode},    // struct
       {refNull(1), kNoneCode},    // array
       {refNull(2), kNoFuncCode},  // signature

test/unittests/wasm/function-body-decoder-unittest.cc

@@ -2142,6 +2142,19 @@ TEST_F(FunctionBodyDecoderTest, NullRefGlobals) {
       &sig, {WASM_GLOBAL_SET(0, WASM_REF_NULL(kNoneCode)), WASM_LOCAL_GET(0)});
 }
 
+TEST_F(FunctionBodyDecoderTest, NullExternRefGlobals) {
+  WASM_FEATURE_SCOPE(gc);
+  ValueType nullExternRefs[] = {kWasmNullExternRef, kWasmNullExternRef,
+                                kWasmNullExternRef};
+  FunctionSig sig(1, 2, nullExternRefs);
+  builder.AddGlobal(kWasmNullExternRef);
+  ExpectValidates(&sig, {WASM_GLOBAL_GET(0)});
+  ExpectValidates(&sig,
+                  {WASM_GLOBAL_SET(0, WASM_LOCAL_GET(0)), WASM_LOCAL_GET(0)});
+  ExpectValidates(&sig, {WASM_GLOBAL_SET(0, WASM_REF_NULL(kNoExternCode)),
+                         WASM_LOCAL_GET(0)});
+}
+
 TEST_F(FunctionBodyDecoderTest, NullFuncRefGlobals) {
   WASM_FEATURE_SCOPE(gc);
   ValueType nullFuncRefs[] = {kWasmNullFuncRef, kWasmNullFuncRef,

test/unittests/wasm/module-decoder-unittest.cc

@@ -189,6 +189,7 @@ struct ValueTypePair {
     {kFuncRefCode, kWasmFuncRef},                  // --
     {kNoFuncCode, kWasmNullFuncRef},               // --
     {kExternRefCode, kWasmExternRef},              // --
+    {kNoExternCode, kWasmNullExternRef},           // --
     {kAnyRefCode, kWasmAnyRef},                    // --
     {kEqRefCode, kWasmEqRef},                      // --
     {kI31RefCode, kWasmI31Ref},                    // --

test/unittests/wasm/subtyping-unittest.cc

@@ -129,13 +129,14 @@ TEST_F(WasmSubtypingTest, Subtyping) {
   constexpr ValueType numeric_types[] = {kWasmI32, kWasmI64, kWasmF32, kWasmF64,
                                          kWasmS128};
   constexpr ValueType ref_types[] = {
-      // TODO(mliedtke): Add externref
-      kWasmFuncRef, kWasmEqRef,       kWasmI31Ref,  // --
-      kWasmDataRef, kWasmArrayRef,    kWasmAnyRef,  // --
-      kWasmNullRef, kWasmNullFuncRef,               // --
-      refNull(0),   ref(0),                         // struct
-      refNull(2),   ref(2),                         // array
-      refNull(11),  ref(11)                         // signature
+      kWasmFuncRef,   kWasmEqRef,          // --
+      kWasmDataRef,   kWasmArrayRef,       // --
+      kWasmI31Ref,    kWasmAnyRef,         // --
+      kWasmExternRef, kWasmNullExternRef,  // --
+      kWasmNullRef,   kWasmNullFuncRef,    // --
+      refNull(0),     ref(0),              // struct
+      refNull(2),     ref(2),              // array
+      refNull(11),    ref(11)              // signature
   };
 
 // Some macros to help managing types and modules.
@@ -192,6 +193,8 @@ TEST_F(WasmSubtypingTest, Subtyping) {
     }
 
     for (ValueType ref_type : ref_types) {
+      const bool is_extern =
+          ref_type == kWasmExternRef || ref_type == kWasmNullExternRef;
       const bool is_any_func = ref_type == kWasmFuncRef ||
                                ref_type == kWasmNullFuncRef ||
                                ref_type == refNull(11) || ref_type == ref(11);
@@ -199,7 +202,7 @@ TEST_F(WasmSubtypingTest, Subtyping) {
       // Concrete reference types, i31ref and dataref are subtypes of eqref,
       // externref/funcref/anyref/functions are not.
       SUBTYPE_IFF(ref_type, kWasmEqRef,
-                  ref_type != kWasmAnyRef && !is_any_func);
+                  ref_type != kWasmAnyRef && !is_any_func && !is_extern);
       // Struct/array types are subtypes of dataref.
       SUBTYPE_IFF(ref_type, kWasmDataRef,
                   ref_type == kWasmDataRef || ref_type == kWasmArrayRef ||
@@ -215,16 +218,17 @@ TEST_F(WasmSubtypingTest, Subtyping) {
       // Each reference type is a subtype of itself.
       SUBTYPE(ref_type, ref_type);
       // Each non-func, non-extern reference type is a subtype of anyref.
-      SUBTYPE_IFF(ref_type, kWasmAnyRef, !is_any_func);
+      SUBTYPE_IFF(ref_type, kWasmAnyRef, !is_any_func && !is_extern);
       // Only anyref is a subtype of anyref.
       SUBTYPE_IFF(kWasmAnyRef, ref_type, ref_type == kWasmAnyRef);
-      // TODO(mliedtke): Improve test coverage for externref.
-      // Only externref is a subtype of externref.
-      NOT_SUBTYPE(kWasmExternRef, ref_type);
+      // Only externref and nullexternref are subtypes of externref.
+      SUBTYPE_IFF(ref_type, kWasmExternRef, is_extern);
+      // Only nullexternref is a subtype of nullexternref.
+      SUBTYPE_IFF(ref_type, kWasmNullExternRef, ref_type == kWasmNullExternRef);
       // Each nullable non-func, non-extern reference type is a supertype of
       // nullref.
       SUBTYPE_IFF(kWasmNullRef, ref_type,
-                  ref_type.is_nullable() && !is_any_func);
+                  ref_type.is_nullable() && !is_any_func && !is_extern);
       // Only nullref is a subtype of nullref.
       SUBTYPE_IFF(ref_type, kWasmNullRef, ref_type == kWasmNullRef);
       // Only nullable funcs are supertypes of nofunc.
@@ -348,8 +352,9 @@ TEST_F(WasmSubtypingTest, Subtyping) {
       UNION(type, type, type);
       INTERSECTION(type, type, type);
       if (type == kWasmFuncRef || type == kWasmNullFuncRef || type == ref(11) ||
-          type == refNull(11)) {
-        // functypes don't share the same type hierarchy as anyref.
+          type == refNull(11) || type == kWasmExternRef ||
+          type == kWasmNullExternRef) {
+        // func and extern types don't share the same type hierarchy as anyref.
         INTERSECTION(type, kWasmAnyRef, kWasmBottom);
         continue;
       }
@@ -377,12 +382,30 @@ TEST_F(WasmSubtypingTest, Subtyping) {
           kWasmEqRef.AsNonNull());
     UNION(kWasmDataRef, kWasmArrayRef, kWasmDataRef);
     UNION(kWasmI31Ref.AsNonNull(), kWasmArrayRef, kWasmEqRef);
+    UNION(kWasmAnyRef, kWasmNullRef, kWasmAnyRef);
+    UNION(kWasmExternRef, kWasmNullExternRef, kWasmExternRef);
+    UNION(kWasmFuncRef, kWasmNullFuncRef, kWasmFuncRef);
+
+    INTERSECTION(kWasmExternRef, kWasmEqRef, kWasmBottom);
+    INTERSECTION(kWasmExternRef, kWasmDataRef, kWasmBottom);
+    INTERSECTION(kWasmExternRef, kWasmI31Ref.AsNonNull(), kWasmBottom);
+    INTERSECTION(kWasmExternRef, kWasmArrayRef, kWasmBottom);
+    INTERSECTION(kWasmExternRef, kWasmNullRef, kWasmBottom);
+    INTERSECTION(kWasmExternRef, kWasmFuncRef, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmEqRef, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmDataRef, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmI31Ref, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmArrayRef, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmNullRef, kWasmBottom);
+    INTERSECTION(kWasmNullExternRef, kWasmExternRef, kWasmNullExternRef);
+    INTERSECTION(kWasmNullExternRef, kWasmExternRef.AsNonNull(), kWasmBottom);
 
     INTERSECTION(kWasmFuncRef, kWasmEqRef, kWasmBottom);
     INTERSECTION(kWasmFuncRef, kWasmDataRef, kWasmBottom);
     INTERSECTION(kWasmFuncRef, kWasmI31Ref.AsNonNull(), kWasmBottom);
     INTERSECTION(kWasmFuncRef, kWasmArrayRef, kWasmBottom);
     INTERSECTION(kWasmFuncRef, kWasmNullRef, kWasmBottom);
+    INTERSECTION(kWasmFuncRef, kWasmNullExternRef, kWasmBottom);
     INTERSECTION(kWasmNullFuncRef, kWasmEqRef, kWasmBottom);
     INTERSECTION(kWasmNullFuncRef, kWasmDataRef, kWasmBottom);
     INTERSECTION(kWasmNullFuncRef, kWasmI31Ref, kWasmBottom);
@@ -390,6 +413,8 @@ TEST_F(WasmSubtypingTest, Subtyping) {
     INTERSECTION(kWasmNullFuncRef, kWasmNullRef, kWasmBottom);
     INTERSECTION(kWasmNullFuncRef, kWasmFuncRef, kWasmNullFuncRef);
     INTERSECTION(kWasmNullFuncRef, kWasmFuncRef.AsNonNull(), kWasmBottom);
+    INTERSECTION(kWasmNullFuncRef, kWasmNullExternRef, kWasmBottom);
+
     INTERSECTION(kWasmEqRef, kWasmDataRef, kWasmDataRef);
     INTERSECTION(kWasmEqRef, kWasmI31Ref, kWasmI31Ref);
     INTERSECTION(kWasmEqRef, kWasmArrayRef, kWasmArrayRef);